My latest garage sale find is a projectile of a 75MM canon. Does anyone have any information, I have done an internet search and it is leaving me blank. It is 8" OAL, 2.940" diameter, the base has a 4" deep hole drilled into it that is 1 1/2" diameter with threads near the base. The markings on the base are “1942 GMC 75MM M61 S2 ???-22586”. I am assuming US manufacture, am I correct? The cavity in the bottom is too large and threaded to be used for a tracer element, in my opinion. Can anyone give any information as to the loading and use. Thank you as always.

What you have found is what’s left of a 75mm M61 A.P.C. shell.
As you can see there are cuts at the top were normaly the cap fits.
On this penatrating cap there is a ballistic cap.
The drivingband is gone.
The hole in the base could be closed with a steel plug with a tracer , empty shell .
But more likely there was a Base Detonating fuze. B.D.M66A1 , shell filled with Explosie D.

This is the "75mm Armor Piercing, Capped- Tracer projectile, M61."
You have the basic part of the projectile, but it is missing the hardened steel cap that gave it the armor piercing quality, and also a sheet metal ballistic cap or windshield that provided better ballistic performance than the blunt cap.
The large threaded opening was for a base fuze which also had a tracer element on the back.

Here is the official description of the projectile from the Army Technical Manual for the 75mm APC-T projectile which was identical except for the type of crimp for the windshield:

"The projectile consists of three parts: a steel body which contains a small charge of explosive D, a steel armor piercing cap, and a 360